Sheet E-310: Accept the MV-P1 Backfill Before Foundation Loading

What this sheet shows

E-310 is the bearing-soil protection / MV pre-installation sheet in the transformer-installation set. Heading 1 is a section marked NTS, titled separate shallow access from the deep MV approach. Heading 2 is the local low-voltage access at a distinct depth. Heading 3 is the installation sequence from SEQ-1 to SEQ-5. The sheet line reads E-310 / PE-P1 / BEARING-SOIL PROTECTION / MV PRE-INSTALLATION. The margin line reads Design Development / 26 SEP 2026 / K&K DATA SERVICE INC., and the title block reads Design Development — Public Edition P1 / 2026-09. Across the section the order is a concrete pier, hatched primary soil bearing beneath the pier, a reserved zone capped S / PER C1, a zone carrying the words retained, transition, and access, and the deep MV-P1 run. That run is labeled MV-P1 / SEQ-1 CIVIL PRE-INSTALL; OD / BEDDING PER C1, and the right-hand column reads 60in cover to duct top. The line under heading 1 states the timing: MV-P1 civil installs the near-foundation ducts and accepts backfill before foundation loading, at SEQ-1..2.

Shallow bearing and the deep approach

Heading 1 separates shallow access from the deep MV approach, and the section draws them as different zones. The reserved zone beside the bearing is capped S / PER C1, and the sheet prints no length for S. The note above the section says to determine S from the bearing and excavation geometry; a 45-degree line alone does not establish S. The next zone carries the stacked words retained, transition, and access. On the deep side the column states 60in cover to duct top, and the run is the SEQ-1 civil pre-install, with OD and bedding per C1 and no duct size on the label. Deep excavation must not undermine the loaded bearing mass. The bearing drawn under the pier is the hatched primary soil bearing. Foundation-support measures are to be provided separately from personnel trench shielding. Later excavation near loaded piers requires a verified C1 support/no-impact arrangement. The line under heading 1 places the MV-P1 ducts and the backfill acceptance at SEQ-1..2, before foundation loading.

Distinct LV depth and the installation sequence

Heading 2 keeps the local low-voltage access at a distinct depth. The recess is an LV local recess study at G-250mm, and no 60in LV-depth requirement is adopted. Two trays end outside the OEM bottom opening; grouped cables turn in. The primary support top remains G+450, and a common indoor/outdoor datum is required. The transverse channel runs left-right across the HV/LV compartments. No pressure is transferred to the terminal enclosure or a nonstructural lid. The 60in figure on the section is the cover to the MV duct top, and the LV note has no 60in LV-depth requirement adopted. The recess remains a study at G-250mm. Heading 3 is the sequence from SEQ-1 to SEQ-5. SEQ-1 protects existing services/ring; civil installs the MV-P1 ducts and elbows. SEQ-2 inspects the support and backfill, records the ducts, and then installs the G-X1 ring crossing. SEQ-3 verifies the bearing and includes four auxiliary piles, takeoffs, and two piers, with cure/accept. SEQ-4 checks OEM bearing and anchors, then places the transformer and bond. SEQ-5 is one MV-crew mobilisation: prove the ducts, pull, terminate, and final tests. The grounding line places G-X1 AFTER MV backfill at SEQ-2, and it requires levels and continuity to be recorded before energising. The grounding reference on that line is E306/E307.

Status

Published at Design Development — Public Edition P1 (title block: 2026-09; margin line: 26 SEP 2026). This is a reference design for study and evaluation. The section is marked NTS. The length of S is per C1, and a 45-degree line alone does not establish S. OD and bedding are per C1. Shallow-foundation dimensions are to be coordinated with OEM bearing and anchor locations before setting out, and those coordinated dimensions are not printed here. The LV local recess is a study at G-250mm. Later excavation near loaded piers requires a verified C1 support/no-impact arrangement. The source line names OSHA1926.651(i), OEM GA08Sep2026, and shallow-foundation design, and it says to provide site-specific excavation support. Foundation-support measures are stated separately from personnel trench shielding.

Sheet guide — the devices on this drawing

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